This invention relates in general to processes and systems for depositing layers on substrates, and more particularly, processes and systems for electroplating metal-containing layers on those substrates.
Currently semiconductor devices are requiring higher current densities for operation while still resisting electromigration or other reliability problems. Copper is being investigated as being a possible alternative to current aluminum or aluminum-copper metalization. One of the most promising methods of depositing copper on a substrate is by using plating methods, such as electroplating.
FIG. 1 includes an illustration of a cross-section view of a prior art electroplating system 10. The system 10 includes a chamber 11 with an outlet port 102. The system further includes a cup 12 that has an inlet port 112 for receiving a plating fluid and a diffuser 13 within cup 12. An anode 14 lies between the cup 12 and the diffuser 13. The system 10 further includes a head 15, that has a turntable 151 and clamp fingers 152. The clamp fingers 152 are the cathode for the system 10 and are typically made of platinized titanium. In the operation of the system 10, the plating solution 19 enters the cup 12 through the inlet port 112, flows by the anode 14, at which point ions from the anode 14 are dissolved into the plating solution 19. The plating solution 19 continues to flow up through the diffuser 13 to reach the substrate 20. The plating solution 19 eventually flows over the sides of the cup 12, down between the walls of the cup 12 and the chamber 11, and through the outlet port 102. The anode 14 and clamp fingers 152 are biased to plate the substrate 20.
During operation of this prior art system 10, non-uniform deposition typically occurs as illustrated in FIG. 2. As shown in FIG. 2, the semniconductor device substrate 20 has a base material 22 that can be an insulator, a conductor, or a combination of insulators and conductors with a conductive seed layer 24 overlying the base material 22. Plated material 26 is plated onto the seed layer 24. Note that the substrate 20 is loading, into system 10 upside down. In FIG. 2, the substrate has been turned upright so that layer 26 faces the top of FIG. 2. As shown in FIG. 2, the deposition of the plated material 26 is typically thicker near the edge of the substrate 20 and thinner near its center point. This nonuniform deposition causes problems, particularly if the plated material 26 is to be chemically mechanically polished. Polishing typically removes material faster near the center and slower near the edges of the substrate. The combination of the thicker portion of the plated material 26 near the edge of the substrate 20 and the lower polishing rate near the edge accentuates the nonuniformity of the plated material 26 after polishing. During polishing, too much of the underlying base material 22 is removed due to non-ideal polishing selectivity or a ring of residual material is left around the edge of the substrate 20, where neither are desired.
Electrical robber plates are used in plating printed circuit board substrates. The robber plate is attached to the board and is destructively removed by cutting the piece of the board having the robber plate.
A need exists to create a system that is either more uniform in deposition or is capable of plating slightly more material near the center of the substrate compared to its edges to compensate for the accelerated polishing typically seen near the center of a substrate.